Everyone who has used carbon paper for copying knows of its disadvantages. It smudges, it dirties the fingers, each sheet gradually deteriorates in efficiency, and it is time consuming to position the carbon paper accurately between the original and copy sheets. These factors led to the search for a substitute, and about 45 years ago, carbonless copy paper was developed.
There are generally two types of carbonless copy technology, mechanical transfer type and chemical.
In the mechanical transfer type carbonless paper technology, the undersurface (back side) of a top sheet is coated with a carbon paper like film. Pressure on the top surface (front side) of the top sheet simply transfers the film to the top surface (front side) of a bottom sheet disposed directly below (underlying the top sheet. Many airline tickets employ a mechanical transfer type carbonless technology.
In the chemical type carbonless paper technology, the back surface (back side) of a top sheet of paper (the "original") is coated with a layer of microcapsules that contain a dye in colorless form in a hydrocarbon solvent. The coating on the back side of the top ("original") sheet is usually termed "CB" for carbonless back or coated back. Writing or printing pressure applied to the top surface (front side) of the top sheet breaks the capsules and releases the dye, which reacts with a clay or phenolic resin coating on the top surface (front side) of a second, underlying paper sheet (the "copy") located directly below the original sheet to produce a visible image of the writing or printing applied to the original on the copy. The coating on the front side of the copy sheet is usually termed "CF" for carbonless front or coated front.
More particularly, the National Cash Register Company of Dayton, Ohio, introduced their NCR ("No Carbon Required") paper in 1954. NCR, or pressure-sensitive paper is based on the principle of coating the under surface (back side) of the top sheet of paper ("original") with a dried emulsion of colorless dye held in microcapsules which are ruptured by the force of writing or printing pressure applied to the front side of the sheet. The released dye is reacted with a reagent on the front surface of an underlying copy sheet which changes the dye to a colored (typically violet, blue or black) image of the writing or printing.
In NCR paper, and its progeny, the color forming chemicals held on the undersurface (back side) of the top (first, original) sheet are typically grouped under the nomenclature "CB", standing for "coated back". The reacting materials on the top surface (front side) of the second (copy) sheet are grouped under the nomenclature "CF", standing for "coated front".
A variation of the chemical carbonless copy technology is employed in the making of more than one copy from an original. In making the first copy, the back side of the first, original sheet is coated with CB carbonless treatment, and the front side of the second (first copy) sheet is coated with CF carbonless treatment. Second, and subsequent, copies can be made at the same time by coating the undersurface (back side) of the second (copy) sheet with CB treatment and coating the top surface (front side) of a third (second copy) sheet with CF treatment, and so forth depending upon how many copies are desired to be produced. The pressure of writing or printing on the top surface of the first, original sheet breaks the CB capsules on the undersurface of the first and second sheets, as a result of which their content of color formers (dyes) and solvent is absorbed into the CF coating (e.g., clay) on the front surface of the second and third sheets, where the color formers are converted to a colored (contrasting with the base color of the paper) image either by a change in pH or by oxidation.
A further variation in the use of chemical carbonless copy technology is employed in the making of a carbonless copy, or copies. Herein, the original, first sheet is not coated, and may be plain paper. The front side of the second, underlying copy sheet is coated with a mixture of CB and CF treatments. The mixture is known as "SC", or "Self-Contained" coating. Mechanical pressure applied (by writing) through the first sheet causes the CB capsules on the front side of the second sheet to rupture, releasing their dye to react with the CF material on the front side of the second sheet. Examples of this variation are found in checkbooks wherein a copy of the check is disposed directly underlying the original.
While carbonless paper, such as has been described above, filled a long felt need for replacing carbon paper, there remains a field of usage which has remained unaddressed for the past 45 years, that is the need for producing a copy of both (front and back) sides of an original form or document. Consider for example, a Federal Tax Return (Internal Revenue Service Form 1040). Information is entered by the taxpayer on both (front and back) sides of the form. Typically, the form is filled out by hand (e.g., written in pen), and the taxpayer must expend additional effort in the making of photocopies of both sides of the form. Alternatively, the information on both sides of the form can be manually transcribed onto both sides of another, duplicate form for recordkeeping purposes. Alternatively, carbon paper could be employed, by carefully positioning a duplicate form under the original form as one side is filled out (with the carbon paper in place therebetween), and then repositioning the form for copying under the original form as the other side is filled out (again, with the carbon paper therebetween). Any of these techniques are entirely unsatisfactory, time consuming, and unnecessary in light of the present invention.